Magazine Editing: How to Develop and Manage a Successful Publication, by John Morrish.

Magazine Editing explores the multi-faceted magazine editing profession--including "the role of the editor both as a journalist, having to provide information and entertainment for readers, and as a manager, expected to lead and supervise successfully the development of a magazine or periodical" (Amazon description). It is written by John Morrish.

The book helps would-be editors to enter the industry and existing editors to
polish their skills. Chapter topics include:

The book also explores the ethical aspects of magazine editing, with appendices
containing the National Union of Journalists Code of Conduct and Press Complaints
Commission Code of Practice. Figures throughout the book offer insight into
budgeting, scheduling, and production.

Magazine Editing is published by Routledge (288 pages, paperback) and is in its second edition. It is available for $31.69 on the Editors Only "Books" page under the "Books on Editing" heading.